An ablative heatshield, as presently formulated for atmospheric entry or re-entry by a space vehicle, is often a rigid structure and, for some missions, requires that the structure be easily packaged, stowed and deployed when that stage of the space vehicle is launched. This is often inconvenient. Use of larger deployable aerodynamic decelerators will allow for heavier payloads to be delivered, but still launched in available systems.
An existing flexible TPS material, such as AFRSI (advanced flexible refractory silicon insulation) cannot survive the heating rates required for a hypersonic inflatable aerodynamic decelerator (HIAD). Existing, rigid TPS material is inflexible and cannot be stowed and deployed for the HIADs.
An existing, rigid TPS material is often difficult to use in the design of a rigid entry vehicle. For example, PICA is not used on the Orion vehicle because of thermo-structural issues when the vehicle serves as a system with the TPS carrier structure. A flexible, ablative TPS, produced according to the invention, would not present this issue because the material is compliant.
Huy Tran et al, in “Silicone Impregnated Reusable Ceramic Ablators For MARS Follow-on Missions,” AIAA Meeting Paper No. 96-1819 (New Orleans Jun. 17-20, 1996), have discussed several thermal characterization experiments performed on different formulations of a thermal ablator material, silicone impregnated reusable ceramic ablators (“SIRCA”), under conditions that approximate the conditions anticipated for a Mars surface landing. Among other observations, the authors found that the formulations of SIRCA characteristically belong to one of three regimes: (i) a first regime, associated with heat flux densities below 150 Watts/cm′, where the SIRCA surface does not recede or undergo phase transformation; (ii) a second regime, associated with heat flux densities in a range of 150-270 Watts/cm′, where the surface does not recede but some of the interior material undergoes a phase change, which appears on or near the surface; and (iii) a third regime, associated with flux densities greater than 270 Watts/cm′, where surface recession and mass loss occur. SIRCA, like PICA, is rigid and requires a tile-like manufacturing and assembly approach in order to enable missions that use large area heatshieds. SIRCA also cannot meet the requirement of a deployable heatshield.
What is needed is a flexible, ablative TPS material that can be deployed in flight near the target to form a large, blunt shape, conformable to a vehicle shape and providing aerodynamic drag during hypervelocity atmospheric flight, without perishing from heating from the bow shock wave that envelops the body. Also needed is a compliant TPS material that is easily to manufacture and attach to space vehicles, that is unaffected by deflections, by differences in thermal expansion, or by contraction of the other material, and that is suitable for use on windward and/or leeward surfaces of conventional robotic and re-entering space vehicles. The material should be capable of withstanding heat fluxes in the range of 40-270 Watts/cm′. Conventional TPS materials are unlikely to satisfy all these needs.